This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A131537 #27 Jul 20 2024 20:11:06
%S A131537 0,5,25,83,219,221,2270,11020,18843,192915,271978,743748,1039315,
%T A131537 13873203,14060685
%N A131537 Exponent of least power of 2 having exactly n consecutive 3's in its decimal representation.
%C A131537 No more terms < 28*10^6.
%H A131537 Popular Computing (Calabasas, CA), <a href="/A094776/a094776.jpg">Two Tables</a>, Vol. 1, (No. 9, Dec 1973), page PC9-16.
%e A131537 a(3) = 83 because 2^83 (= 9671406556917033397649408) is the smallest power of 2 to contain a run of exactly 3 consecutive threes in its decimal form.
%t A131537 a = ""; Do[ a = StringJoin[a, "3"]; b = StringJoin[a, "3"]; k = 1; While[ StringPosition[ ToString[2^k], a] == {} || StringPosition[ ToString[2^k], b] != {}, k++ ]; Print[k], {n, 1, 9} ]
%o A131537 (Python)
%o A131537 def a(n):
%o A131537 k, n2, np2 = 1, '3'*n, '3'*(n+1)
%o A131537 while True:
%o A131537 while not n2 in str(2**k): k += 1
%o A131537 if np2 not in str(2**k): return k
%o A131537 k += 1
%o A131537 print([a(n) for n in range(1, 9)]) # _Michael S. Branicky_, May 25 2021
%Y A131537 Cf. A000079.
%K A131537 nonn,base,more
%O A131537 0,2
%A A131537 _Shyam Sunder Gupta_, Aug 26 2007
%E A131537 a(10)-a(12) from _Sean A. Irvine_, Jul 19 2010
%E A131537 a(13)-a(14) from _Lars Blomberg_, Jan 24 2013
%E A131537 a(0)=0 prepended by _Paul Geneau de Lamarlière_, Jul 20 2024